Download LibreCAD
LibreCAD (originally QCad then CADuntu) is a multiplatform open source 2D CAD application. It is based on Qt the leading cross-platform application and UI development framework.
LibreCAD can read DWG files (and others) and it writes DXF files, but can also export projects to SVG, JPG, PNG, PDF and other file formats. It offers support for layers, blocks, splines, polylines, ellipse tools, advanced tangent line & circle tools, transformation tools, an advanced snapping system and more.
LibreCAD is focuses on creating only 2D geometry so it is really fast and lightweight, with an installer of less than 30 MB. The application can be also used from command line. You can use the spacebar to activate the text interface and start giving commands to draw elements.
LibreCAD offers albo functions like undo nad redo, command line calculator, advanced zooming options using keyboard and mouse, drawing text objects, circles, rectangles, arc, lines and others. You can also draw linear, aligned, horizontal detentions.